Author and Astrophysicist

Epistolary Higgs

Over the summer, the big physics news was the discovery of a new particle which is, in all likelihood, the Higgs boson. I’m not going to give a detailed explanation of what the Higgs is and how it was found — Bruce Bassett wrote a great post about that here, there’s a more detailed post here, and a set of more detailed posts here.

Instead, here’s an e-mail exchange I had with a friend about the Higgs — he had a question, and I answered it, but there’s a bit more to it than that…From: Stuart To: Adam Becker Subject: Why, why should ANYBODY believe in the Higgs boson?

Like Omar Sharif materializing out of the shimmering desert as a man on a camel in “Lawrence of Arabia,” the elusive boson has been coming slowly into view since last winter, as the first signals of its existence grew until they practically jumped off the chart.

I’m not asking for a scientific explanation, let alone evidence. I am asking why hundreds of thousands of intelligent people believe in this thing without a shadow of a sub-atomic particle of proof. The rationale I understand is one of those “truths of coherence”: “well, if we didn’t posit its existence, none of the rest of our cosmology and cosmogony would in the end make any sense.”

Conspiracy? That I can understand too: a veritable conjuration des clercs. Unless of course the National Lampoon started it — and deriving “boson” from “bozo” is entirely in their style of wit.

Dennis Overbye at the NYT is quite good, but he may have gone slightly overboard with the Lawrence of Arabia stuff. I’ll see what I can do to convince you about the Higgs.

Here’s the basic idea: the laws of nature as we understand them, at the smallest scales, are probabilistic rather than deterministic. We can’t say whether a particular event will occur in a particle accelerator at a particular time — we can only say what the odds are. This means that particle “discovery” is a tricky business: no matter what you see in your particle detector, you can always say that there is no new particle, and that you’re just getting really lucky (or unlucky) with the interactions between particles you already know about. How many times does a pair of dice have to come up sixes before you decide that they’re weighted? In particle physics, the answer is that you roll the dice until the odds that they’re not weighted are about one in three million; then you can say the dice are weighted (i.e. you’ve found a new particle). Over at the LHC, the dice have been coming up sixes for months, but only now have the dice have been rolled enough times for particle physicists to comfortably say that the dice are weighted. That’s what Overbye was trying to get across with his Lawrence of Arabia imagery.

Why did we think the Higgs was there in the first place? You’re basically spot-on with the idea that it’s a “truth of coherence.” We have something called the Standard Model of particle physics, which is a large and complicated theory (or, if you prefer, a collection of mutually consistent small and simple theories) that successfully explains everything we’ve ever seen in a particle accelerator, and does a nice job of explaining nearly all observed physical phenomena. The Standard Model demands that the Higgs boson exist, and since the Standard Model is right about everything else, it’s quite plausible that there is a Higgs. So, as far as your question goes, that’s the best answer I can give you without going into a real scientific explanation.

But I’ve left something out. That phrase I just used, “nearly all observed physical phenomena,” is a little bit of a cheat. It’s true, as far as it goes: there are only four things that I can think of in the whole universe that the Standard Model doesn’t explain. But one of those four is gravity, and two of the other three things — dark matter and dark energy — are the biggest outstanding mysteries in cosmology. And reconciling gravity with quantum field theory (the language of the Standard Model) is unarguably the most important theoretical challenge in particle physics. (String theory was developed almost exclusively to solve the latter problem.) So we know, and have known since its inception, that the Standard Model is not complete. But the Standard Model is a victim of its own success. Because it’s so good at explaining everything we see in particle accelerators,1 it’s hard to figure out exactly how to extend the Standard Model to explain gravity and the other stuff it doesn’t account for.

So the search for the Higgs has an additional importance: if the Higgs doesn’t behave the way we think it should, or if it isn’t there at all, or if there’s more than one, that’s a hint of physics beyond the Standard Model. The worst-case scenario is that the LHC finds a perfectly normal Higgs and doesn’t find anything else: that wouldn’t tell us anything fundamentally surprising about the way nature works, and we’re actively looking for a surprise.

Thanks so much for a lucid and dramatic explanation that almost completely makes sense to me — and for ignoring the extravagances of my rhetoric (which I’m certainly not going to subdue, as you will see).

Most interesting is your fifth paragraph (on the “additional importance” of the search). Would I be wrong to read it thus? — If the HiggsBo turns up in the LHC as expected, face washed, shoes tied, all vaccinations in order, good SAT scores, ready to make its yearning parents proud of their fecundity (in producing such an offspring) and their acumen (in predicting all these fine and sterling qualities), THE PARENTS WILL BE DEVASTATED. Dammit! Just another fuckin particle! Normal child, well socialized, nothing to cure or accommodate, nothing to break up the family or change the world for…. What the parents REALLY want is a misfit or monster, a lusus naturae, in short a DISCONFIRMATION providing “a hint of physics beyond the SM” that will trigger an earthquake in business-as-usual. Right?

If so, that’s exciting and comprehensible, and fits in with the banal theories of scientific change I’m silently quoting. It’s also pleasantly romantic. Happy love/normal science has no history! Every unhappy family/wrecked paradigm is tragically, fascinatingly unhappy in its own way! Faust doesn’t just err because he strives; he strives to err!

But baby, you’d better be damn sure not to let the Great American Public or their clownish representatives catch a hint of this interesting erotic narrative, or they will defund every physics department and particle collider in the country and sow the sites with salt. ESPECIALLY not in an election year that’s going as badly as this one.

(“There will be no war. But in the struggle for peace not one stone will be left standing upon another.” Okay, I stole that from John le Carré.)

Yes, your reading of my fifth paragraph is spot-on (and hilarious). If the Higgs shows up with nary a hair out of place on its head, we’ll be deeply disappointed. There is, right now, the barest hint that the Higgs is in fact misbehaving, and you can see particle physicists salivating publicly on their blogs at the idea that the Higgs has a skinned knee and dirt on its face. We know the SM is wrong, and what we really want is a wayward Higgs to show us where our mistake might be.

— Adam

Gravity plays no measurable role in particle physics because the stuff involved is so small, and dark matter and dark energy are cosmological phenomena that (so far) don’t have measurable effects on anything smaller than a galaxy. [↵]